But what can we expect from the final 24 episodes of The Big Bang Theory? The sitcom's showrunner and co-executive producer Steve Holland gave an in-depth interview with The Hollywood Reporter about the show's final season, opening up about the difficult task of satisfactorily wrapping up a show that has gained a rabid fanbase across 250-odd episodes.

WHEN THEY FOUND OUT

Holland said the cast and crew weren't aware going into the 12th season that it would be their last - they found out in the second week of production, when one episode had already been filmed and six or seven written. But he said, "We all knew going into this season that there was a chance it could be the end. The cast's deals were up and it had been a long time."

DON'T EXPECT TEARS …

Holland said he doesn't "want the last season to feel melancholy".

"I think it still needs to be a fun, funny year."

And while the creators of another popular sitcom Modern Family have teased that they'll kill off a "significant character" in what's likely to be their final season, Holland has no plans for anything like that. "The DNA of the show is a happy, positive, loving show and I don't think it would feel right to leave this show on a downer note," he said.

Holland and team have a wish list of celebrity guests they're yet to get on the show, but he said he's aware they can't stuff the few remaining episodes with celebrity cameos just to scratch that itch.

"We want to be careful of not just making it a parade of guest stars, which is an easy trap to fall into on your last lap. We really want to make sure we focus on our characters and give them the proper ending that they deserve," he said.

Still, he lists nerd icons William Shatner and George Lucas as two he'd love to have on.

Also expect to see returns for stars who've previously appeared on the show: Among them Bob Newhart (Professor Proton), Laurie Metcalf (as Sheldon's mother) and Christine Baranski (as Leonard's mother).

YOUNG SHELDON COULD MAKE A CAMEO
Holland said the team has discussed enlisting the star of spin-off show Young Sheldon, Iain Armitage, to appear on the final season. They could have Sheldon "discover a videotape he made as a kid as a fun way to use (Armitage)."

Sheldon and Amy got married at the end of last season. Picture: CBS

EXPECT RELATIONSHIP DRAMAS

Sheldon and Amy are now married, which means him "having to deal with now having in-laws for the first time".

"Sheldon and Amy working together and being married is going to be a thing that plays out throughout the season," said Holland, who also hinted we'll see them have their "first big post-marriage fight".

Long-married Leonard and Penny, meanwhile, will finally tackle whether or not they want to have children. It's a topic that's been skirted around in the past, according to Holland, but it's definitely "something they're going to be dealing with this season".

As for Howard and Bernadette, things are going great - but it can be "overwhelming", especially for her.

"She's got this job she's successful at and she has two kids at home and how do you balance all of those things and still maintain any sort of sense of individuality?" Holland said.